The present invention relates to implantable electrode leads generally, and more particularly to leads adapted for use in the coronary sinus.
Recently, an increased interest in pacing the left atrium and ventricle of the heart has led to a resurgence of interest in location of cardiac pacing leads in the coronary sinus, great vein, or other cardiac vein. To this end, the use of guidewire placed leads, as disclosed in U.S. Pat. No. 3,769,984 issued to Muench, has resurfaced, leading to the development of a number of coronary sinus pacing leads intended to be advanced into a desired location within the cardiac vasculature over a guidewire. Some examples of such leads are disclosed in U.S. Pat. No. 6,033,414 issued to Tockman et al., U.S. Pat. No. 5,935,160 issued to Auricchio et al., and U.S. Pat. No. 5,304,218 issued to Alferness. As an alternative to advancing a lead to a desired position by means of a guidewire, it has also been proposed to fashion the tip of a lead with a preformed curve, so that the tip of the lead itself may be used to steer the lead through the cardiac vasculature. Such a lead is disclosed in U.S. Pat. No. 6,006,122 issued to Smits. In addition to renewed interest in locating leads within the cardiac veins, there has been significant developmental effort expended on solving the problem of maintaining a lead in a desired location in the cardiac veins. One group of solutions to this problem has been to provide the lead with a preformed set of bends or curves in the lead body, temporarily straightened by stylet, which upon removal of the stylet expand to wedge the lead within the cardiac veins. Examples of leads of this type are disclosed in U.S. Pat. No. 4,488,561 issued to Doring, U.S. Pat. No. 4,454,888 issued to Gold and U.S. Pat. No. 4,057,067 issued to Lajos, An alternative set of mechanisms for location of leads has been to provide an electrode, which is either configured to be wedged in the cardiac veins, or which is adapted to be expanded into contact with the wall of the cardiac veins. Such electrodes are disclosed in U.S. Pat. No. 6,006,122 issued to Smits, U.S. Pat. No. 5,224,491 issued to Mehra, and U.S. Pat. No. 5,991,668 issued to Leinders.
The present invention is directed toward a lead adapted to be located within the cardiac vasculature, which may be readily steered to a desired location within the cardiac vasculature and thereafter securely located at a desired pacing site. The present invention accomplishes these desired results by means of a lead provided with an improved electrode assembly located at its distal tip. The electrode assembly includes a fixation helix and a guidewire-like projection, both extending from the distal end of the lead body. The fixation helix, which may serve as all or part of the active electrode surrounds a structure corresponding to the distal end of a conventional guidewire (hereafter referred to as the xe2x80x9cguidewire tipxe2x80x9d). The fixation helix is mounted around the guidewire tip in such a fashion that the sharpened tip of the helix lies closely adjacent to the guidewire tip, in a region of the guidewire tip which is sufficiently flexible to allow it to be moved away from the sharpened tip of the helix. The guidewire tip, which may be provided with a preformed curve at its distal end, is employed to navigate the lead through the cardiac vasculature in a fashion similar to the navigation of a catheter and guidewire in combination or a guidewire alone. Upon reaching the desired location within the cardiac vasculature, the lead may be rotated to screw one or more turns of the fixation helix into heart or blood vessel tissue, the flexibility of the guidewire tip allowing it to move away from the sharpened tip of the helix during the process of affixing the lead to the tissue.